Historically, natural cork has been utilized as the primary closure for wine bottles. There are, however, several disadvantages associated with the use of natural cork. For example, natural cork generally has variable properties with respect to, among other things, color, flavor neutrality, shrinkage, expansion, crumbling, ease of insertion, ease of removal, seal formation, and gas permeability. The variability of these properties is undesirable. Moreover, natural cork is susceptible to contamination by various molds which are difficult to eliminate and tend to taint the bottled wine's flavor and aroma.
As a result of the disadvantages associated with natural cork, numerous attempts have been made to develop replacement thermoplastic-based bottle closures. Unfortunately, most development efforts to date have experienced shortcomings, particularly in terms of production cost, product performance, and consumer acceptance. For example, many commercially available synthetic closures have a tendency to noticeably taint bottled wine products.
As way of background, one common type of synthetic closure is disclosed in U.S. Pat. No. 4,363,849 to Paisley et al. This patent discloses the production of synthetic closures having a natural cork-like appearance, wherein the synthetic material is a common polyolefin, such as an ethylene vinyl acetate copolymer (EVA). Similarly, U.S. Pat. No. 4,188,457 to Throp discloses another plastic composition useful for making synthetic closures. The thermoplastic composition disclosed by Throp also comprises an EVA copolymer as a major component. EVA copolymers, however, are undesirable for making synthetic closures because these materials are not able to quickly expand back to its original formed shape after being compressed by, for example, the corker jaws of a bottling machine.
Another type of synthetic closure is disclosed in U.S. Pat. No. 5,904,965 to Noel et al. More specifically, this patent discloses a synthetic closure made by a co-extrusion molding process that produces a continuous rod having a foamed core surrounded by a peripheral non-foamed skin layer. (The formed continuous rod is then cut into smaller cylinders that constitute individual synthetic closures.) A problem associated with this type of synthetic closure, however, is that there is no protective skin layer at either of its ends. As a result, gas permeation through the foamed core is much greater than synthetic closures having protective outer skin layers.
Still another type of synthetic closure is the kind disclosed in U.S. Pat. No. 5,317,047 to Sabate et al. This patent discloses, among other things, a composition useful for making synthetic closures, wherein the composition constitutes a mixture of three principal components; namely, (1) powder and particles of natural cork; (2) expandable plastic microspheres of a methyl methacrylate-acrylonitrile copolymer; and (3) a polyurethane or acrylic binding agent. As disclosed, a selected amount of such a three-part composition is introduced into a cylindrical shaped mold, heat is then rapidly applied in order to expand the plastic microspheres thereby causing the composition to fill the mold, and finally the expanded composition is allowed to slowly cool in order to properly set the binding agent.
The resulting natural/synthetic closure made in accordance with U.S. Pat. No. 5,317,047 to Sabate et al. has many characteristics consistent with that of natural cork; however, it does not possess a protective outer skin like that of many other types of synthetic closures. Because there is no protective outer skin, the resulting synthetic closure suffers from at least three drawbacks. First, the synthetic closure is substantially less durable than a synthetic closure having a protective outer skin (e.g., the pulling action associated with removing the synthetic closure from a bottle using a traditional corkscrew can cause cracking and disintegration that shortens the synthetic closure's useful life). Second, the synthetic closure is more amenable to “scoring” when compressed by the corker jaws of a bottling machine than a synthetic closure encapsulated by a protective outer skin. Finally, and because there is no outer protective skin layer, gas permeation through the natural/synthetic closure is generally greater than synthetic closures having protective outer skin layers.
To date, one of the most successful synthetic closures, which overcomes many of the disadvantages associated with natural cork and other prior art synthetic closures, are the synthetic closures manufactured by Supreme Corq (Kent, Wash. U.S.A.). Specifically, U.S. Pat. Nos. 5,480,915; 5,496,862; 5692,629; 5,710,184; 5,855,287; and 6,127,437 all to Burns and assigned to Supreme Corq (and are all expressly incorporated herein by reference), disclose various synthetic closures for removable insertion into bottles and containers. These synthetic closures are made from formulations that comprise a “thermoplastic elastomer” material, wherein the thermoplastic elastomer preferably comprises a styrene block copolymer. Such synthetic closures generally have an outer skin layer surrounded by a foamed interior, and have proved to be a significant improvement over both natural corks and other types of commercially available synthetic closures.
Although the synthetic closures disclosed in the Supreme Corq patents are superior in many respects as compared to other types of bottle or container closures, technical problems still exist with these and other types of synthetic closures, especially in terms overall performance characteristics. For example, and as noted above, many commercially available synthetic closures have relatively low resistance to oxygen permeation into the container, which can result in oxidation and thus tainting of the wine product. In addition, there is still much room for improvement with respect to having the right combination of physical properties associated with each synthetic closure including, for example, shape (length, width, diameter), weight, density, hardness, insertion force, extraction or removal force, compression force, compression recovery time, cork screw penetration force, and flaking. Accordingly, and while significant advances have been made in the field of synthetic closures for removable insertion into bottles and containers, there is still a need in the art for new and improved synthetic closures and manufacturing processes relating thereto. The present invention fulfills these needs and provides for further related advantages.